DESCRIPTION

The pkg-config program is used to retrieve information about installed libraries in the
system. It is typically used to compile and link against one or more libraries. Here is
a typical usage scenario in a Makefile:
program: program.c
cc program.c $(pkg-config --cflags --libs gnomeui)
pkg-config retrieves information about packages from special metadata files. These files
are named after the package, and has a .pc extension. On most systems, pkg-config looks
in /usr/lib/pkgconfig,/usr/share/pkgconfig,/usr/local/lib/pkgconfig and
/usr/local/share/pkgconfig for these files. It will additionally look in the colon-
separated (on Windows, semicolon-separated) list of directories specified by the
PKG_CONFIG_PATH environment variable.
The package name specified on the pkg-config command line is defined to be the name of the
metadata file, minus the .pc extension. If a library can install multiple versions
simultaneously, it must give each version its own name (for example, GTK 1.2 might have
the package name "gtk+" while GTK 2.0 has "gtk+-2.0").
In addition to specifying a package name on the command line, the full path to a given .pc
file may be given instead. This allows a user to directly query a particular .pc file.

OPTIONS

The following options are supported:
--modversion
Requests that the version information of the libraries specified on the command
line be displayed. If pkg-config can find all the libraries on the command line,
each library's version string is printed to stdout, one version per line. In this
case pkg-config exits successfully. If one or more libraries is unknown, pkg-config
exits with a nonzero code, and the contents of stdout are undefined.
--version
Displays the version of pkg-config and terminates.
--atleast-pkgconfig-version=VERSION
Requires at least the given version of pkg-config.
--help Displays a help message and terminates.
--print-errors
If one or more of the modules on the command line, or their dependencies, are not
found, or if an error occurs in parsing a .pc file, then this option will cause
errors explaining the problem to be printed. With "predicate" options such as
"--exists" pkg-config runs silently by default, because it's usually used in
scripts that want to control what's output. This option can be used alone (to just
print errors encountered locating modules on the command line) or with other
options. The PKG_CONFIG_DEBUG_SPEW environment variable overrides this option.
--short-errors
Print short error messages.
--silence-errors
If one or more of the modules on the command line, or their dependencies, are not
found, or if an error occurs in parsing a a .pc file, then this option will keep
errors explaining the problem from being printed. With "predicate" options such as
"--exists" pkg-config runs silently by default, because it's usually used in
scripts that want to control what's output. So this option is only useful with
options such as "--cflags" or "--modversion" that print errors by default. The
PKG_CONFIG_DEBUG_SPEW environment variable overrides this option.
--errors-to-stdout
If printing errors, print them to stdout rather than the default stderr
--debug
Print debugging information. This is slightly different than the
PKG_CONFIG_DEBUG_SPEW environment variable, which also enable "--print-errors".
The following options are used to compile and link programs:
--cflags
This prints pre-processor and compile flags required to compile the packages on the
command line, including flags for all their dependencies. Flags are "compressed" so
that each identical flag appears only once. pkg-config exits with a nonzero code if
it can't find metadata for one or more of the packages on the command line.
--cflags-only-I
This prints the -I part of "--cflags". That is, it defines the header search path
but doesn't specify anything else.
--cflags-only-other
This prints parts of "--cflags" not covered by "--cflags-only-I".
--libs This option is identical to "--cflags", only it prints the link flags. As with
"--cflags", duplicate flags are merged (maintaining proper ordering), and flags for
dependencies are included in the output.
--libs-only-L
This prints the -L/-R part of "--libs". That is, it defines the library search path
but doesn't specify which libraries to link with.
--libs-only-l
This prints the -l part of "--libs" for the libraries specified on the command
line. Note that the union of "--libs-only-l" and "--libs-only-L" may be smaller
than "--libs", due to flags such as -rdynamic.
--libs-only-other
This prints the parts of "--libs" not covered by "--libs-only-L" and "--libs-only-
l", such as "--pthread".
--variable=VARIABLENAME
This returns the value of a variable defined in a package's .pc file. Most packages
define the variable "prefix", for example, so you can say:
$ pkg-config --variable=prefix glib-2.0
/usr/--define-variable=VARIABLENAME=VARIABLEVALUE
This sets a global value for a variable, overriding the value in any .pc files.
Most packages define the variable "prefix", for example, so you can say:
$ pkg-config --print-errors --define-variable=prefix=/foo \
--variable=prefix glib-2.0
/foo
--print-variables
Returns a list of all variables defined in the package.
--uninstalled
Normally if you request the package "foo" and the package "foo-uninstalled" exists,
pkg-config will prefer the "-uninstalled" variant. This allows compilation/linking
against uninstalled packages. If you specify the "--uninstalled" option, pkg-config
will return successfully if any "-uninstalled" packages are being used, and return
failure (false) otherwise. (The PKG_CONFIG_DISABLE_UNINSTALLED environment
variable keeps pkg-config from implicitly choosing "-uninstalled" packages, so if
that variable is set, they will only have been used if you pass a name like "foo-
uninstalled" on the command line explicitly.)
--exists--atleast-version=VERSION--exact-version=VERSION--max-version=VERSION
These options test whether the package or list of packages on the command line are
known to pkg-config, and optionally whether the version number of a package meets
certain constraints. If all packages exist and meet the specified version
constraints, pkg-config exits successfully. Otherwise it exits unsuccessfully. Only
the first VERSION comparing option will be honored. Subsequent options of this type
will be ignored.
Rather than using the version-test options, you can simply give a version
constraint after each package name, for example:
$ pkg-config --exists 'glib-2.0 >= 1.3.4 libxml = 1.8.3'
Remember to use --print-errors if you want error messages. When no output options
are supplied to pkg-config, --exists is implied.
--validate
Checks the syntax of a package's .pc file for validity. This is the same as
--exists except that dependencies are not verified. This can be useful for package
developers to test their .pc file prior to release:
$ pkg-config --validate ./my-package.pc
--msvc-syntax
This option is available only on Windows. It causes pkg-config to output -l and -L
flags in the form recognized by the Microsoft Visual C++ command-line compiler, cl.
Specifically, instead of -Lx:/some/path it prints /libpath:x/some/path, and instead
of -lfoo it prints foo.lib. Note that the --libs output consists of flags for the
linker, and should be placed on the cl command line after a /link switch.
--define-prefix--dont-define-prefix
These options control whether pkg-config overrides the value of the variable prefix
in each .pc file. With --define-prefix, pkg-config uses the installed location of
the .pc file to determine the prefix. --dont-define-prefix prevents this behavior.
The default is usually --define-prefix.
When this feature is enabled and a .pc file is found in a directory named
pkgconfig, the prefix for that package is assumed to be the grandparent of the
directory where the file was found, and the prefix variable is overridden for that
file accordingly.
If the value of a variable in a .pc file begins with the original, non-overridden,
value of the prefix variable, then the overridden value of prefix is used instead.
This allows the feature to work even when the variables have been expanded in the
.pc file.
--prefix-variable=PREFIX
Set the name of the variable that pkg-config overrides instead of prefix when using
the --define-prefix feature.
--static
Output libraries suitable for static linking. That means including any private
libraries in the output. This relies on proper tagging in the .pc files, else a
too large number of libraries will ordinarily be output.
--list-all
List all modules found in the pkg-config path.
--print-provides
List all modules the given packages provides.
--print-requires
List all modules the given packages requires.
--print-requires-private
List all modules the given packages requires for static linking (see --static).

ENVIRONMENTVARIABLES

PKG_CONFIG_PATH
A colon-separated (on Windows, semicolon-separated) list of directories to search
for .pc files. The default directory will always be searched after searching the
path; the default is libdir/pkgconfig:datadir/pkgconfig where libdir is the libdir
for pkg-config and datadir is the datadir for pkg-config when it was installed.
PKG_CONFIG_DEBUG_SPEW
If set, causes pkg-config to print all kinds of debugging information and report
all errors.
PKG_CONFIG_TOP_BUILD_DIR
A value to set for the magic variable pc_top_builddir which may appear in .pc
files. If the environment variable is not set, the default value '$(top_builddir)'
will be used. This variable should refer to the top builddir of the Makefile where
the compile/link flags reported by pkg-config will be used. This only matters when
compiling/linking against a package that hasn't yet been installed.
PKG_CONFIG_DISABLE_UNINSTALLED
Normally if you request the package "foo" and the package "foo-uninstalled" exists,
pkg-config will prefer the "-uninstalled" variant. This allows compilation/linking
against uninstalled packages. If this environment variable is set, it disables
said behavior.
PKG_CONFIG_ALLOW_SYSTEM_CFLAGS
Don't strip -I/usr/include out of cflags.
PKG_CONFIG_ALLOW_SYSTEM_LIBS
Don't strip -L/usr/lib or -L/lib out of libs.
PKG_CONFIG_SYSROOT_DIR
Modify -I and -L to use the directories located in target sysroot. this option is
useful when cross-compiling packages that use pkg-config to determine CFLAGS and
LDFLAGS. -I and -L are modified to point to the new system root. this means that a
-I/usr/include/libfoo will become -I/var/target/usr/include/libfoo with a
PKG_CONFIG_SYSROOT_DIR equal to /var/target (same rule apply to -L)
PKG_CONFIG_LIBDIR
Replaces the default pkg-config search directory, usually
/usr/lib/pkgconfig:/usr/share/pkgconfig.
PKG_CONFIG_$PACKAGE_$VARIABLE
Overrides the variable VARIABLE in the package PACKAGE. The environment variable
should have the package name and package variable upper cased with non-alphanumeric
characters converted to underscores. For example, setting
PKG_CONFIG_GLADEUI_2_0_CATALOGDIR will override the variable "catalogdir" in the
"gladeui-2.0" package.

PKG-CONFIGDERIVEDVARIABLES

pkg-config sets a few metadata variables that can be used in .pc files or queried at
runtime.
pc_path
The default search path used by pkg-config when searching for .pc files. This can
be used in a query for the pkg-config module itself itself:
$ pkg-config --variable pc_path pkg-config
pcfiledir
The installed location of the .pc file. This can be used to query the location of
the .pc file for a particular module, but it can also be used to make .pc files
relocatable. For instance:
prefix=${pcfiledir}/../..
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include
pc_sysrootdir
The sysroot directory set by the user. When the sysroot directory has not been set,
this value is /. See the PKG_CONFIG_SYSROOT_DIR environment variable for more
details.
pc_top_builddir
Location of the user's top build directory when calling pkg-config. This is useful
to dynamically set paths in uninstalled .pc files. See the PKG_CONFIG_TOP_BUILD_DIR
environment variable for more details.

WINDOWSSPECIALITIES

The pkg-config default search path is ignored on Windows. Instead, the search path is
constructed by using the installed directory of pkg-config and then appending
lib\pkgconfig and share\pkgconfig. This can be augmented or replaced using the standard
environment variables described above.

AUTOCONFMACROS

PKG_CHECK_MODULES(VARIABLE-PREFIX,MODULES[,ACTION-IF-FOUND[,ACTION-IF-NOT-FOUND]])
The macro PKG_CHECK_MODULES can be used in configure.ac to check whether modules
exist. A typical usage would be:
PKG_CHECK_MODULES([MYSTUFF], [gtk+-2.0 >= 1.3.5 libxml = 1.8.4])
This would result in MYSTUFF_LIBS and MYSTUFF_CFLAGS substitution variables, set to
the libs and cflags for the given module list. If a module is missing or has the
wrong version, by default configure will abort with a message. To replace the
default action, specify an ACTION-IF-NOT-FOUND. PKG_CHECK_MODULES will not print
any error messages if you specify your own ACTION-IF-NOT-FOUND. However, it will
set the variable MYSTUFF_PKG_ERRORS, which you can use to display what went wrong.
Note that if there is a possibility the first call to PKG_CHECK_MODULES might not
happen, you should be sure to include an explicit call to PKG_PROG_PKG_CONFIG in
your configure.ac.
Also note that repeated usage of VARIABLE-PREFIX is not recommended. After the
first successful usage, subsequent calls with the same VARIABLE-PREFIX will simply
use the _LIBS and _CFLAGS variables set from the previous usage without calling
pkg-config again.
PKG_PREREQ(MIN-VERSION)
Checks that the version of the pkg-config autoconf macros in use is at least MIN-
VERSION. This can be used to ensure a particular pkg-config macro will be
available.
PKG_PROG_PKG_CONFIG([MIN-VERSION])
Defines the PKG_CONFIG variable to the best pkg-config available, useful if you
need pkg-config but don't want to use PKG_CHECK_MODULES.
PKG_CHECK_MODULES_STATIC(VARIABLE-PREFIX,MODULES[,ACTION-IF-FOUND[,ACTION-IF-NOT-FOUND]])
Enables static linking through --static prior to calling PKG_CHECK_MODULES.
PKG_CHECK_EXISTS(MODULES,[ACTION-IF-FOUND],[ACTION-IF-NOT-FOUND])
Check to see whether a particular set of modules exists. Similar to
PKG_CHECK_MODULES(), but does not set variables or print errors.
Similar to PKG_CHECK_MODULES, make sure that the first instance of this or
PKG_CHECK_MODULES is called, or make sure to call PKG_CHECK_EXISTS manually.
PKG_INSTALLDIR(DIRECTORY)
Substitutes the variable pkgconfigdir as the location where a module should install
pkg-config .pc files. By default the directory is $libdir/pkgconfig, but the
default can be changed by passing DIRECTORY. The user can override through the
--with-pkgconfigdir parameter.
PKG_NOARCH_INSTALLDIR(DIRECTORY)
Substitutes the variable noarch_pkgconfigdir as the location where a module should
install arch-independent pkg-config .pc files. By default the directory is
$datadir/pkgconfig, but the default can be changed by passing DIRECTORY. The user
can override through the --with-noarch-pkgconfigdir parameter.
PKG_CHECK_VAR(VARIABLE,MODULE,CONFIG-VARIABLE,[ACTION-IF-FOUND],[ACTION-IF-NOT-FOUND])
Retrieves the value of the pkg-config variable CONFIG-VARIABLE from MODULE and
stores it in VARIABLE. Note that repeated usage of VARIABLE is not recommended as
the check will be skipped if the variable is already set.

METADATAFILESYNTAX

To add a library to the set of packages pkg-config knows about, simply install a .pc file.
You should install this file to libdir/pkgconfig.
Here is an example file:
# This is a comment
prefix=/home/hp/unst # this defines a variable
exec_prefix=${prefix} # defining another variable in terms of the first
libdir=${exec_prefix}/lib
includedir=${prefix}/include
Name: GObject # human-readable name
Description: Object/type system for GLib # human-readable description
Version: 1.3.1
URL: http://www.gtk.org
Requires: glib-2.0 = 1.3.1
Conflicts: foobar <= 4.5
Libs: -L${libdir} -lgobject-1.3
Libs.private: -lm
Cflags: -I${includedir}/glib-2.0 -I${libdir}/glib/include
You would normally generate the file using configure, so that the prefix, etc. are set to
the proper values. The GNU Autoconf manual recommends generating files like .pc files at
build time rather than configure time, so when you build the .pc file is a matter of taste
and preference.
Files have two kinds of line: keyword lines start with a keyword plus a colon, and
variable definitions start with an alphanumeric string plus an equals sign. Keywords are
defined in advance and have special meaning to pkg-config; variables do not, you can have
any variables that you wish (however, users may expect to retrieve the usual directory
name variables).
Note that variable references are written "${foo}"; you can escape literal "${" as "$${".
Name: This field should be a human-readable name for the package. Note that it is not the
name passed as an argument to pkg-config.
Description:
This should be a brief description of the package
URL: An URL where people can get more information about and download the package
Version:
This should be the most-specific-possible package version string.
Requires:
This is a comma-separated list of packages that are required by your package. Flags
from dependent packages will be merged in to the flags reported for your package.
Optionally, you can specify the version of the required package (using the
operators =, <, >, >=, <=); specifying a version allows pkg-config to perform extra
sanity checks. You may only mention the same package one time on the Requires:
line. If the version of a package is unspecified, any version will be used with no
checking.
Requires.private:
A list of packages required by this package. The difference from Requires is that
the packages listed under Requires.private are not taken into account when a flag
list is computed for dynamically linked executable (i.e., when --static was not
specified). In the situation where each .pc file corresponds to a library,
Requires.private shall be used exclusively to specify the dependencies between the
libraries.
Conflicts:
This optional line allows pkg-config to perform additional sanity checks, primarily
to detect broken user installations. The syntax is the same as Requires: except
that you can list the same package more than once here, for example "foobar =
1.2.3, foobar = 1.2.5, foobar >= 1.3", if you have reason to do so. If a version
isn't specified, then your package conflicts with all versions of the mentioned
package. If a user tries to use your package and a conflicting package at the same
time, then pkg-config will complain.
Libs: This line should give the link flags specific to your package. Don't add any flags
for required packages; pkg-config will add those automatically.
Libs.private:
This line should list any private libraries in use. Private libraries are
libraries which are not exposed through your library, but are needed in the case of
static linking. This differs from Requires.private in that it references libraries
that do not have package files installed.
Cflags:
This line should list the compile flags specific to your package. Don't add any
flags for required packages; pkg-config will add those automatically.

AUTHOR

pkg-config was written by James Henstridge, rewritten by Martijn van Beers, and rewritten
again by Havoc Pennington. Tim Janik, Owen Taylor, and Raja Harinath submitted suggestions
and some code. gnome-config was written by Miguel de Icaza, Raja Harinath and various
hackers in the GNOME team. It was inspired by Owen Taylor's gtk-config program.